The recent spread of smartphones and tablets has led to a drastic increase in radio traffic. Fifth-generation mobile communication systems (5G) are being researched and developed in order to cope with the increase in traffic.
An access scheme called Orthogonal Frequency Division Multiple Access (OFDMA), in which many narrow-band carriers (subcarriers) are arranged orthogonally (orthogonal multiple access), is used in Long Term Evolution (LTE) and LTE-Advanced (LTE-A) downlinks. However, non-orthogonal multiple access techniques are being investigated extensively as access techniques for 5G. In non-orthogonal multiple access, signals that do not have orthogonality are transmitted with the assumption that interference cancellation or reception processing such as maximum likelihood estimation will be carried out by a receiver. Downlink Non-Orthogonal Multiple Access (DL-NOMA) is being examined as non-orthogonal multiple access for downlinks (PTL 1, PTL 2). In DL-NOMA, a base station device (also called “evolved Node B” (eNB) or “base station”) adds (superposition coding) and transmits modulation symbols addressed to multiple terminal devices (also called “User Equipment” (UE), “mobile station devices”, “mobile stations”, or “terminals”). At this time, the transmit power allocated to each modulation symbol is determined in light of the receive power (reception quality) at the multiplexed terminal devices, the modulation and coding scheme (MCS; modulation scheme and coding rate), and the like. Each terminal device includes a CodeWord-level Interference Canceller (CWIC), and can extract only the modulation symbol addressed to itself by decoding the signals addressed to other terminal devices contained in the multiplexed transmit signal, generating replicas of the signals addressed to the other terminal devices, and canceling those from the received signal.
Having a terminal device apply Symbol-Level IC (SLIC) or Maximum Likelihood Detection (MLD) instead of CIVIC is &so being investigated (NPL 1). Although signals addressed to other terminal devices sometimes cannot be completely eliminated, applying SLIC or MLD does make it possible to implement DL-NOMA without using information pertaining to signals addressed to other terminal devices (coding rate, resource allocation information, and the like).